1. Field of the Invention
The present invention relates to a light source package used in such optical systems as a photocopier, a laser printer, or similar image forming apparatus, and to an image forming apparatus using the light source package.
2. Description of the Related Art
Conventional image forming apparatus have a light source and a lens supported by a lens support member in the housing and compensate the lens for changes in focal length and refractive index resulting from the thermal expansion and contraction of the lens by utilizing the thermal expansion and contraction of the housing. Examples of such packages are disclosed in Japanese laid-open Patent Publication (Kokai) Nos. Hei 3(1991)-179420 and Hei 3(1991)-179421.
However, while such conventional apparatus compensate the lens for changes in the focal length and refractive index of the lens when an ambient temperature changes, the ambient temperature change also causes the optical axis of the lens to deviate from the normal optical axis position if the lens and the lens support member are made from materials with different thermal expansion coefficients. Such a deviation in optical axis prevents images from being properly formed.
This is particularly a problem in a multi-beam image forming apparatus in which optical beams from plural laser sources are converted into optical beams for image formation by using corresponding lenses so that the plural laser beams simultaneously scan the object in parallel. When the optical axis of each lens becomes offset from the axis of the light source, the scanned positions on the object tend to move close to or apart from each other, and normal image formation is thus prevented.